Plant sterol and plant stanol, which is the saturated form thereof, are known to reduce the total cholesterol concentration and the low-density lipoprotein-cholesterol concentration in blood, and they are considered safe as food products. Because plant sterols are contained in vegetable oil, soy beans, wheat, etc., human beings frequently ingest them, but the amounts ingested are very small, and therefore the expectation of utilizing plant sterols as a food ingredient has increased in recent years.
There are problems, however, because plant sterols are solids at normal temperature (melting point approximately 140° C.) and they are insoluble in water and poorly soluble in oil-based ingredients, that if powdered plant sterols are merely added to various types of food products, the particles of the plant sterol powder coagulate, resulting in a food product with a gritty texture. Therefore, various methods for utilizing plant sterols in food products have been studied.
For example, the following methods have been proposed to obtain an oil-in-water emulsified product such as mayonnaise, etc., that contains plant sterols: a method for obtaining an emulsified product by dissolving the plant sterol in oil to create an oil phase, separately forming a water phase from water and enzyme-treated egg yolk, and then adding the water phase to the oil phase with thorough stirring and mixing (patent document 1); a method for obtaining an oil-in-water emulsified product by heating, mixing and agitating plant sterol, a phospholipid (lecithin), a polyvalent alcohol, water and ethanol to homogenize then, and then gradually adding a food oil or fat thereto (Patent Document 2): and a method for obtaining an emulsified product by using a complex as an emulsifier, where the complex is prepared by dissolving phospholipid and sterol in an organic solvent, and removing the organic solvent to precipitate the phospholipid and the sterol simultaneously (patent document 3).    Patent Document 1: Japanese Patent Application Laid-open No. 2002-171931    Patent Document 2: Japanese Patent Application Laid-open No. 2001-000117    Patent Document 3: Japanese Patent Application Laid-open No. H04-149194